The timecourse of expression aftereffects.

Adaptation to facial expressions produces aftereffects that bias perception of subsequent expressions away from the adaptor. Studying the temporal dynamics of an aftereffect can help us to understand the neural processes that underlie perception, and how they change with experience. Little is known about the temporal dynamics of the expression aftereffect. We conducted two experiments to measure the timecourse of this aftereffect. In Experiment 1 we examined how the size of the aftereffect varies with changes in the duration of the adaptor and test stimuli. We found that the expression aftereffect follows the classic timecourse pattern of logarithmic build-up and exponential decay that has been demonstrated for many lower level aftereffects, as well as for facial identity and figural face aftereffects. This classic timecourse pattern suggests that the adaptive calibration mechanisms of facial expression are similar to those of lower level visual stimuli, and is consistent with a perceptual locus for the adaptation aftereffect. We also found that aftereffects could be generated by as little as 1 s of adaptation, and in some conditions lasted for as long as 3200 ms. We extended this last finding in Experiment 2, exploring the longevity of the expression aftereffect by adding a stimulus-free gap of varying duration between adaptation and test. We found that significant expression aftereffects were still present 32 s after adaptation. The persistence of the expression aftereffect suggests that they may have a considerable impact on day-to-day expression perception.